Measuring physical properties of fluids is of immense industrial importance. Fluid flow is determined by properties like viscosity, elasticity and studying them can provide interesting insights about their internal structures and how they can be changed by environmental factors. Usually, these properties are measured using an instrument called Rheometer which is expensive, time consuming and requires larger volume of fluids.
In a recent study published in Advanced Functional Materials Dr.Arijit Ghosh, Debayan Dasgupta, Malay Pal from India, and Konstantin Morozov from Israel, along with Prof Ambarish Ghosh from Centre for NanoScience and Engineering, IISc and Prof Alex Lehshansky from Technion – Israel Institute of Technology have demonstrated how helical nano-machines can be used as an indicator of fluid properties. The helical nano-machines, about a micron in length and few hundred nanometers in width, were driven using a rotating magnetic field and the local viscosity of the fluid was measured from their swimming dynamics.
They have used this technique to measure the viscosity of simple fluids like water and glycerol. They have also shown how this technique can be extended to fluids with complex structures like Xantham gum, where the fluid becomes thinner with more strain. This technique has been further used to study viscosity change at interfaces as denser fluids mix with thinner fluids. This method of measuring viscosity at micron scale with high precision can have important biological applications like mapping the viscosity inside a living cell or real-time measurement of changes in blood. It may also have industrial applications for studying interface properties during mixing at a micron scale.
Figure: a) SEM of a nanomachine (scale bar: 500 nm). b) Schematic of the microfluidic chamber placed inside a triaxial Helmholtz coil, and c) Schematic and experimental photographs of a precessing nanomachine (scale bar: 2 um). INSET: a) Method to estimate moment angle by applying a large dc magnetic field and subsequently imaging the nanomachine. b) Two different methods of integrating magnetic materials on the helix. c) Estimated viscosity versus shear rate for various samples: water, glycerol diluted by 50% water, xanthan gum solutions in water at 100, 300, and 500 ppm.